Thats because in the l99 the 1st gear is really aggressive. A little higher than 4.00. When you put it in sport mode it starts off the car in 2nd.

this and also when the trans is shifting itself it will upshift into higher gears at a steady cruise/light acceleration.
which means it has to downshift if you floor it and that slows the response time compared to tapshifting and manually holding a lower gear and keeping the rpm higher.

that 1st gear (and even 2nd) is tricky to tapshift correctly without hitting the rev limiter due to the relative slowness of the shift.
if you wait to tapshift until a few hundred under the redline, the rpm increase will beat the shift into second and you hit the rev limiter.